1. Field of the Invention
The present invention relates to a temperature detection system for measuring the temperature of a power semiconductor device with a high degree of precision.
2. Description of the Related Art
An apparatus in which a power semiconductor device having a large heating value such as a power semiconductor module or the like is incorporated, is typically provided with a temperature detection system as part of the apparatus. The following illustrates uses of temperature signals detected by and output from the temperature detection system. First, it is used for overheat protection of the power semiconductor device. If the above-mentioned temperature signal is used, control to prevent or detect that the power semiconductor device reaches a predetermined temperature or more is possible. As another example, the above-mentioned temperature signal can be used when an apparatus in which the above-mentioned power semiconductor device is incorporated performs feedback control. In this case, since a control signal to the power semiconductor device or the like is defined based on the above-mentioned temperature signal, it is possible to generate a control signal with reduced loss.
As discussed above, the temperature signal detected by and output from the temperature detection system is useful in overheat protection or to reduce losses in feedback control. Then, as this temperature signal approaches high precision, i.e., as it becomes closer to the highest temperature value of the power semiconductor device, it is preferable to make it possible to perform proper overheat protection and to generate a control signal with reduced loss.
Patent Document 1 discloses a temperature detection system including a thermistor arranged in a position spaced from the power semiconductor device, and an on-chip temperature sensor closer to the highest temperature generating part in the power semiconductor device than the above-mentioned thermistor. This temperature detection system uses the thermistor to perform temperature detection with high S/N ratio when the temperature of the power semiconductor device is so low that the overheat protection is not needed. On the other hand, if the temperature of the power semiconductor device is high and close to temperature at which the overheat protection is needed, temperature close to the temperature of the power semiconductor device is detected by means of the on-chip temperature sensor. Thus, the temperature detection system disclosed in Patent Document 1 changes the temperature detection methods according to the temperature of the power semiconductor device.
[Patent Document 1] Japanese Patent Application Laid-Open No. 07-135731
[Patent Document 2] Japanese Patent Application Laid-Open No. 07-153920
[Patent Document 3] Japanese Patent Application Laid-Open No. 07-075349
[Patent Document 4] Japanese Patent Application Laid-Open No. 07-107784
[Patent Document 5] Japanese Patent Application Laid-Open No. 08-322240
[Patent Document 6] Japanese Patent Application Laid-Open No. 10-337084
As described in Patent Document 1, between the temperature output from the thermistor or on-chip temperature sensor and the highest temperature in the power semiconductor device, if a position at which the temperature sensor is provided and a position (highest temperature point) in the power semiconductor device, the position indicating the highest temperature during normal operation are different, there is a temperature difference. Then, the temperature difference varies according to the value of a load on the power semiconductor device or the like (e.g., current or voltage). However, a temperature signal output from the temperature detection system described in Patent Document 1 or any other patent document does not consider that the temperature difference varies. Therefore, it is considered that the temperature signal generated by the temperature detection system described in Patent Document 1 or the like may not accurately reflect the temperature of the power semiconductor device. As a result, there is a problem that proper overheat protection cannot be performed or a control signal with reduced loss cannot be generated. The temperature difference can be eliminated by placing the on-chip temperature sensor at the highest temperature point of the power semiconductor device. However, in such a case, there often occur problems that it adversely affects the performance of the power semiconductor device and it makes wire bonding in the assembly process difficult.